Energy in various forms is required in industrial production and is often produced from high-grade carriers of primary energy, such as gas and oil. The increasing shortages and the growing political insecurity of the supply increasingly require that these energy carriers be substituted by solid fuels. For this reason, new technologies are needed for a transformation of the solid fuels into a form in which they can be substituted for the traditional energy carriers in existing processes.
The pollution involved in the use of solid fuels must be reliably avoided, particularly because the shortage of primary energy necessitates an increasing use of coals having high ash and sulfur contents.
In dependence on the nature of a given process step carried out to produce a given product, energy is needed by industry in various forms, for instance, as heating steam, as high-temperature heat in a different form, or as a clean fuel gas, which can be burned without adversely affecting the quality of the product.
While energy in various forms, such as fuel gas and steam, can be produced separately, the capital requirements and operating expenses involved in that practice are not justified in industrial plants of usual size. Besides, an operation of independent plants for the conversion of energy involves high losses and an increased expenditure for the protection of the environment.
In order to avoid the disadvantages involved in the separate production of energy in different forms, a process for the simultaneous production of fuel gas and steam has been proposed, in which coal of any desired quality is gasified in a fluidized bed and the gasification residue is burned to produce steam (Processing, November 1980, page 23).
This process is an advance in a promising direction although its throughput rate related to given reactor dimensions is low and owing to the process conditions selected, particularly for the gasifying stage, the flexibility regarding the relative rates at which fuel gas and steam can be produced is low. Besides, this process does not provide a solution to the problems encountered in the required purification of fuel gas, particularly as regards the removal of sulfur and of the noxious by-products formed by the purification of fuel gas.